1. Field of the Invention
This invention relates to viscosity drift control in overbased detergents, principally overbased sulfonates and phenates. The invention move specifically relates to the method and composition for controlling viscosity drift in a detergent in storage prior to incorporation in a finished lubricating oil.
2. Background and Discussion of the Prior Art
Overbased detergents are extensively used in lubricating oils. Generally, the overbased detergent is shipped and stored prior to incorporation in the lubricating oil. The storage and shipping conditions often expose the detergent to temperatures substantially above ambient for long periods of time. It was found that overbased detergents would, over time, and under elevated temperatures, increase in viscosity. This viscosity increase or drift caused the overbased detergent to be out of specification with the initially specified viscosity, and in certain cases the viscosity of the stored overbased detergent had sufficiently increased so as not to be useful for blending in the lubricating oil. The lubricating oil art was directed away from overbased detergents having high viscosities because of handling and filter ability problems, as discussed in U.S. Pat. No. 5,011,618 to Papke et al and U.S. Pat. No. 4,387,033 to Lenack et al.
Overbased calcium sulfonate detergents were generally required to have a viscosity of no more than about 200 to 250 cSt at 100.degree. C., but after several weeks of storage particularly under elevated temperatures, the detergent viscosity would drift to 400 cSt at 100.degree. C. or more. The increased or high viscosity overbased calcium sulfonate was then unsuitable for blending and use in lubricating oils.
While it was known in the lubricating oil art to add certain alkyl phenols and vegetable oils to finished blended lubricating oils to enhance certain performance characteristics, it was not known that limited amounts of such additives when added to an overbased detergent per se in contradistinction to a lubricating oil effectively controlled viscosity drift in long term storage of the detergent prior to blending the detergent in a lubricating oil.
The art directed to processes for producing overbased detergents recognized that certain alkyl phenols could be used as co-promoters, as disclosed in Burnop, U.S. Pat. No. 4,104,180. Where alkyl phenols were used as co-promoters, the overbased detergent co-promoter reaction product had no effect as a viscosity drift control agent, The alkyl phenol co-promoter detergent would undergo substantial viscosity drift in storage.
The overbased detergent art desired a viscosity drift control agent or system which reduced or eliminated viscosity drift of the detergent in storage.
The term "viscosity drift" as used hereinbefore and hereinafter means the change (increase) in viscosity over time. The term "viscosity drift control" as used hereinbefore and hereinafter means the reduction in the change (increase) in viscosity over time. The term "additive amount(s)" as used hereinbefore and hereinafter means about 0.1 to 5.0% by weight.